Prototype chain

Now that we know what prototypal inheritance is let us explore the prototype chain.

Object.prototype - parent of all objects#

At the top of the prototypal inheritance hierarchy is the Object.prototype object. It is the root object or parent of all objects. When we create an object literal, its prototype is the Object.prototype object.

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const obj = {};

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console.log(Object.getPrototypeOf(obj) === Object.prototype);

// true

You can run the above code in the Replit below:

We didn't define any properties on the obj object. But we can still call some methods on it.

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const obj = {};

​

console.log(obj.toString()); // [object Object]

You can run the above code in the Replit below:

We didn't define a method named toString on the obj object; how is it accessible in the code example above? You guessed it: it is defined on the Object.prototype object, and as Object.prototype is the prototype of obj, the properties defined on Object.prototype are inherited by obj, toString being one of them.

Objects created in this way are instances of the Object constructor function. We can also define obj as shown below:

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const obj = new Object();

This has the same effect: it creates an empty object. As discussed in the previous lesson, functions have a prototype property that points to an object that serves as the "prototype" of all instances of that function when that function is invoked as a "constructor". So, the Object.prototype object serves as the "prototype" of all objects created via new Object() or through object literal notation.

At this point, you might ask: isn't toString callable on all objects? Yes, it is; some objects inherit it from the Object.prototype object, while other objects, such as arrays, inherit it from their prototype, i.e., the Array.prototype object, which overrides the toString implementation defined in Object.prototype.